1. Field of the Invention
This invention relates to an in situ method of cleaning soil, particularly sand, gravel, clay, and the like, and aqueous solutions such as water, that have been contaminated with, e.g., metal ions such as lead, chromium, silver and the like, sulfur-containing compounds, cyanide-containing compounds, and the like. The method relies on the formation of an aqueous slurry, the addition in separate steps of a detergent and an additive to promote the growth of indigenous microorganisms, and the regulation of the temperature at which these steps are conducted to thereby reduce the presence of metals, sulfur compounds, cyanide compounds and/or other contaminants in the soil and/or water. The extraction of these and other contaminants with the detergent may be repeated until their content is reduced to a level such that the remaining amount may be removed by concentration and/or adsorption and/or degradation by microorganisms indigenous to the soil and/or water.
2. Description of the Background
Various methods have been employed in the past to remove contaminants from contaminated solids such as soil. U.S. Pat. No. 4,781,944 to Jones describes a method and apparatus for detoxifying heavy metals such as chromium, arsenic, barium, cadmium, lead, mercury, selenium, silver, nickel, zinc, copper, and others, from contaminated soil, sludge, ashes, and the like. The method fixes the metals with carbon. It does so by heating a soil sample with a carbon-containing material to a temperature below the temperature for complete volatilization of most heavy metals while inhibiting the formation of oxides to produce a carbon bonded metal char residue, then cooling the char residue in the absence of air to insure that the residue will not combust, and then cooling to ambient temperature. The thus obtained residue is non-leachable since it heats to encapsulate the heavy metals by bonding to a carbon material. The metals are affixed to the carbon which may then be disposed of (see, column 4, lines 21-28 and 53-62 of Jones for description of combustion conditions and pyrolysis chamber).
U.S. Pat. No. 4,789,475 to Harte et al. discloses a method for treating a bed material with chelating agents and the use of this agent to remove a broad range of toxic chemicals from drinking water. The bed material is preferably granulated activated charcoal and the treated bed material is utilized in a water filtration device. Chelating agents, such as EDTA, are embedded in the bed material by application of a polymer/chelating agent-containing solution to the charcoal, rinsing and drying the bed material, treating it with an acidic solution and rinsing and drying.
U.S. Pat. No. 4,998,848 to Hansen describes an in situ method and apparatus for removing gaseous or vaporizable contaminants from a solid material without wholesale removal of the contaminated material. A perforated container with granules of charcoal providing a large surface for adsorption is inserted in the contaminated soil area. A cryogenic liquid, such as liquid nitrogen, is introduced in the container to cool the granules. The removal of contaminants from the soil is then accomplished by allowing for the gaseous or vaporized contaminants to flow out of the ground and into the container's perforations. The contaminants are thus adsorbed onto the cooled surface of the charcoal, and the container is removed from the ground when approaching saturation.
U.S. Pat. No. 4,460,292 to Durham et al. has claims limited to an in situ method of containing a contaminated liquid such as waste, hazardous liquids, drilling muds and chemicals by absorbing it into biogenetic silica. However, in the patent, it is indicated that the silica may contain a wide variety of additives such as carbon or activated charcoal (see, column 3, lines 28-32). The biogenetic silica is applied, whether alone or with additives, to the surface of the liquids in bulk or in contained form, such as in pellets. It may be added by gravity or sprayed onto or into the liquids, with or without mixing (see, column 3, lines 39-45).
U.S. Pat. No. 4,585,753 to Scott et al. relates to an aqueous suspension of activated charcoal for use as an in situ agricultural spray. The suspension contains, in addition, a wetting and suspending agent consisting of octylphenoxy(polyethoxyethanol) and a defoaming agent.
U.S. Pat. No. 4,778,628 to Saha et al. discloses and claims a method of disposing waste material that comprises forming a recessed area within the earth, lining it with a layer of zeolite, lining the zeolite with a layer of activated carbonaceous material to form a container, placing the waste material within the cavity, adding a second layer of activated carbonaceous material onto the waste material and a second layer of zeolite thereon. The entire contaminated soil area is buried inside an underground waste barrier structure.
U.S. Pat. No. 4,780,239 to Snyder et al. relates to a method of making an ion-exchange material by implanting an element such as carbon into a ceramic material and oxidizing the carbon to carboxylate or carbonate.
U.S. Pat. No. 2,969,294 to Shyne discloses and claims a method of uniformly extracting uranium into a graphite body to form a fuel block for a homogeneous, graphite-moderated nuclear research reactor.
A study published by the U.S. Department of Commerce (National Technical Information Service No. PB84-123637) funded by the United States Environmental Protection Agency and conducted by Rexnord, Inc. discusses requirements for mobile systems to extract spilled hazardous materials from excavated soils. The study lists the characteristics necessary for an effective extraction fluid. Chief among these characteristics is a solvent possessing low volatility at ambient conditions. A volatile solvent under ambient conditions, such as aqueous ammonia, is not considered a suitable extraction fluid by the above study to decontaminate soil.
Accordingly, there is still a need for a simple and effective method for cleaning contaminated soil such as gravel, sand, clay, and the like, and water, contaminated with metal compounds, sulfur compounds, including sulfhydric acid, and cyanide compounds, that may be easily conducted at the site of a spill and provide a significant reduction in the levels of metal ions such as heavy metal ions, sulfur compounds and cyanide compounds in the soil and in surface and subterranean water layers.